Stopper rod

ABSTRACT

There is provided a refractory mono-block stopper of substantially cylindrical configuration having an upper end, a lower end and an axial bore extending downwardly from the upper end, means being provided in the axial bore at a distance d from the upper end for attachment of the stopper to a lifting mechanism, the stopper being divided into three portions (A,B,C); a first portion (A) extending from the upper end towards the lower end until a distance greater than d, a second portion (B) extending from the first portion (A) towards the lower end and a third portion (C) extending from the second portion (B) and comprising a stopper nose ending at the lower end of the stopper. The stopper of the invention is characterized in that the average section of the second portion (B) is lower than the section of the first portion (A) and the highest section of the third portion (C) is higher than the lowest section of the second portion (B). 
     The stopper of the invention has a significantly reduced weight without any observable loss of strength. It is also noted that since the profile of the stopper can be kept symmetrical around its axis, the stopper does not require extra handwork to be removed from the mold.

FIELD OF THE INVENTION

This invention relates to a stopper used as part of a valve mechanism inthe control of flow of molten material from a vessel through a submergedoutlet. More particularly, it relates to refractory mono-block stoppers,i.e. one piece ceramic stopper rods as currently used to control theflow of molten metal exiting from a nozzle mounted in the bottom of amelt-containing vessel, e.g. ladle or tundish. This is typically appliedin the casting of steel through an opening in the base of the tundishvia nozzles and shrouds into a water-cooled mould.

BACKGROUND OF THE INVENTION

Typically, such stoppers consist of an elongate cylindrical refractoryceramic body of isostatically-pressed graphite/alumina having at thelower end a rounded or tapered profile (the stopper nose) suitable forengagement in the throat of a corresponding exit nozzle, and at theupper end some form of connecting means to fasten the stopper onto anexternal lifting mechanism by which the flow is controlled.

Operation of the stopper is simple in principle. A mechanical liftingsystem is used to vertically lift the stopper rod from a seatingposition on the nozzle to ease or restrict the volume of the moltenmetal flowing through the nozzle. However, in practice, such a stopperrod has to operate under harsh environmental conditions such as beingsubmerged in the molten metal for long periods of time and must be ableto withstand the high thermal shocks encountered in the pouringprocesses.

The cost of a stopper is essentially due to handwork and the quantity ofrefractory material. Attempts have already been made to reduce the costby reducing the weight of the stopper. In such a case, care must betaken to avoid loss of strength. EP-A-625,391 discloses a flutedstopper, the outer surface of which being provided with a number ofaxial grooves. The exterior surface of the stopper has an undulatingcontour comprising alternate lobes and recesses to provide a fluteddesign which is said to retain the strength of a regular cylindricalstopper. However, the time needed to remove the stopper from its complexmould, largely overbalance the economy of refractory material.

It is therefore desirable to provide a stopper with a design allowing touse less refractory material without loss of strength while keeping thehandwork as low as possible. The present invention aims to provide animproved stopper fulfilling these objectives.

SUMMARY OF THE INVENTION

According to one aspect of the present invention there is provided arefractory mono-block stopper of substantially cylindrical configurationhaving an upper end, a lower end and an axial bore extending downwardlyfrom the upper end, means being provided in the axial bore at a distanced (d being at the middle of the attachment means) from the upper end forattachment of the stopper to a lifting mechanism, the stopper beingdivided into three portions (A,B,C); a first portion (A) extending fromthe upper end towards the lower end until a distance greater than d, asecond portion (B) extending from the first portion (A) towards thelower end and a third portion (C) extending from the second portion (B)and comprising a stopper nose ending at the lower end of the stopper.The stopper of the invention is characterized in that the averagesection of the second portion (B) is lower than the section of the firstportion (A) and the highest section of the third portion (C) is higherthan the lowest section of the second portion (B).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a prior art stopper.

FIG. 2 is a schematic view of a stopper according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is based on the observation that the higheststressed point in a stopper is generally located around the means forattachment of the stopper to a lifting mechanism (at a distance which isgenerally greater than d from the upper end). Contrarily to the ideagenerally admitted in the art, the present inventors have perceived thatit is not necessary to have an important thickness of refractorymaterial all along the stopper to ensure that it can withstand the harshworking conditions placed upon it. Therefore, they have retained theconventional thickness of refractory material around the means forattachment of the stopper to a lifting mechanism (first portion) andaround the nose of the stopper (third portion) which must remainsuitable for engagement in the throat of a corresponding exit nozzlewhile reducing the thickness of refractory material in the intermediateportion (second portion) thereby reducing significantly the weight ofthe stopper without any observable loss of strength.

It would be possible to also reduce the dimension of the third portion,however, preferably, the highest section of the third portion (C) ishigher than the average section of the second portion (B) so that thenose of the stopper (third portion) remains suitable for engagement inthe throat of a corresponding conventional exit nozzle.

Advantageously, the first portion A is at least equal to 2 d.

The section of the first portion A must be large enough to provide therequired strength to the stopper around the attachment means. Theskilled person knows from conventional stoppers the range of sectionsthat are suitable for this purpose. The section of this portion cantaper slightly towards the bottom end but preferably, it issubstantially constant.

Preferably the first and third portions are kept as short as possible inorder to increase the saving in material. Advantageously, the firstportion will not exceed a length of 4 to 5 d and the third portion willbe limited to the stopper nose.

The essence of the present invention is thus that the second portion (B)is of reduced thickness with respect to the first (A) and third (C)portions.

The reduction in thickness of the second portion can be embodied by asubstantially concave profile in vertical side-view. According to otherembodiments, the second portion (B) has the form of an hyperboloid or ofa simple taper.

However for the sake of easiness of manufacture and especially ofdemoulding, the second portion (B) comprises preferably a firstsub-portion (B1) extending downwardly from the first portion (A) andhaving a section decreasing progressively and a second sub-portion (B2)extending from the bottom of the first sub-portion (B1) to the bottom ofthe second portion (B) and having a substantially constant section. Inorder to increase the material saving, it is preferred that the sectiondecreases as rapidly as possible in the first sub-portion (B1). Thetaper should be such that the stress at any portion is no greater thanthat close to the attachment; conventional strength of materialscalculation allows to determine the minimum sections necessary toachieve this result.

As is well known with conventional stoppers, the stopper according tothe invention can be used with gas injection means so that a gas,preferably an inert gas, can be injected into the molten metal duringthe casting operations. Generally, in such a case, the gas is introducedinto the axial bore of the stopper which conducts the gas to the lowerend were it can be inject directly in the molten metal through a bore ora porous material.

According to the present invention, all form of attachments can be usedsuch as a copressed metallic or ceramic insert, and the like.

As well known in the art, the stopper can include various parts ofdifferent composition (porous or erosion-resistant composition for thenose, slag resistant composition for a sleeve at the slag line,increased strength or permeability composition around the attachment).

The nose of the stopper of the invention can have any shape suitable forengagement in the throat of a corresponding exit nozzle. Optionally, itcan be coated with a protective coating such as a glaze for example.

The stopper according to this invention can be manufactured according toconventional and well known processes for making refractory mono-blockstoppers; such as isostatic pressing in an appropriate mould anddemoulding, optionally followed by a step of machining the demouldedbody.

One embodiment of the present invention will now be described by way ofexample with reference to the accompanying drawings in which:—

FIG. 1 is a schematic view of a prior art stopper, and

FIG. 2 is a schematic view of a stopper according to the invention.

Turning now to the Figures, there is shown a stopper rod (1) for use inthe control of flow of molten material from a tundish or vessel (notshown). The stopper rod (1) comprises a refractory body having an upperend (2), a lower end (3) and an axial bore (4) having a restrictedportion in its lower region (8). An inert gas such as argon can be fedfrom a gas supply, through the axial bore in the upper region of thestopper rod. Attachment means (5) of the stopper to a lifting mechanism(not shown) are provided in a first portion A of the stopper in theaxial bore (4) at a distance d from the upper end (2).

The third portion C includes the nose (6) which comprises injectionmeans for the inert gas. The gas can be injected directly from the axialbore such as depicted on FIG. 1 or through a part 7 of the nose such asdepicted on FIG. 2.

In the stopper of the prior art (FIG. 1), the second portion B issubstantially cylindrical and has the same thickness as the first A andthird portion C. In the stopper of the invention as depicted on FIG. 2,the second portion (B) has a reduced thickness.

In particular, the portion B has a first sub-portion B1 tapering rapidlyto a reduced section and a second sub-portion B2 of substantiallyconstant section.

The stopper of FIG. 2 has a weight 30% less than the weight of thestopper of FIG. 1 while having equivalent strength.

REFERENCES

-   1. Stopper-   2. Upper end-   3. Lower end-   4. Axial bore-   5. Attachment means-   6. Stopper nose-   7. Porous material-   8. Axial bore in the nose

1. Refractory mono-block stopper of substantially cylindrical configuration comprising an upper end, a lower end and an inner surface defining an axial bore extending from the upper end towards the lower end, an attachment provided in the axial bore at a distance from the upper end, the stopper being divided into a) a first portion extending from the upper end towards the lower end, the first portion having a length longer than the distance and having a first cross-section; b) a second portion extending from the first portion towards the lower end, the second portion comprising a second cross-section, where an average of the second cross-section is smaller than the first section; and c) a third portion extending from the second portion and comprising a stopper nose ending at the lower end of the stopper, the third portion having a third cross-section adjacent to the second portion that is larger than the second cross-section adjacent to the third portion.
 2. Stopper of claim 1, wherein the third cross-section adjacent to the second section is greater than the average of the second cross-section.
 3. Stopper of claim 1, wherein the length of the first portion is at least twice the distance.
 4. Stopper of claim 1, wherein the first cross-section is substantially constant or tapers very slightly downwardly.
 5. Stopper of claim 1, wherein the second portion includes a vertical cross-section from the first portion to the third portion.
 6. Stopper of claim 5, wherein the vertical cross-section is substantially concave.
 7. Stopper of claim 5, wherein the vertical cross-section progressively tapers.
 8. Stopper of claim 5, wherein the vertical cross-section is substantially an hyperboloid.
 9. Stopper of claim 1, wherein the second portion consists of: a) a first sub-portion extending from the first portion and having a first sub-cross-section decreasing progressively; and b) a second sub-portion extending from the first sub-portion and having a second sub-cross-section that is substantially constant.
 10. Stopper of claim 1, wherein the axial bore extends through the first and second portions.
 11. Stopper of claim 1, wherein the stopper nose includes a gas injector.
 12. Stopper of claim 1, wherein at least a part of the stopper nose comprises a porous material.
 13. Stopper of claim 1, wherein the axial bore extends through the first and second portions and at least a part of the third portion. 